Exact same behavior as linked topic, but for Hydroid's tentacles instead of Limbo's stasis.
Reproduction steps in simulacrum:
Losing overguard:
Cast tentacle swarm under an eximus / unit with overguard
Strip overguard from enemy
Enemy continues to move freely until tentacles are recast (enemy leaving and re-entering cast area has no effect).
Gaining overguard:
Cast tentacle swarm under a regular corrupted unit (lancer, crewman, etc) which will be grabbed
Spawn a corrupted ancient which will give the grabbed enemy overguard
Grabbed enemy with overguard continues to be grabbed until recast.